The present invention relates to a storage module for flat postal items having a storage area and an infeed function, which transfers postal items from a stream of postal items into the storage area, and an extraction function, which extracts postal items from the storage area.
With today's postal sorting systems, very large quantities of postal items sometimes have to be sorted and distributed in so-called mail centers and/or larger post offices. By way of example, the average daily amount of post received in Germany is about 80 million letters, which must reach their addressees the very next day or at the latest on the next day but one after posting. Postal items of this kind are, for example, letters. It is characteristic of these postal items that the length and the width of these postal items are generally large compared with their height. There are significant differences between the postal administration authorities of the different national states regarding the definitive dimensions for assigning postal items to this group of “letters”. As well as these size variations, it can also easily be seen that the nature of postal items, even when they are all “letters”, differs considerably from one to another under certain circumstances.
It is therefore easy to imagine that postal automation processes today have to be operated with a high degree of efficiency and, as a result of cost pressure, also with a comparatively low number of operators. To achieve sufficiently large throughput rates in the sorting machines, the postal items are conveyed through the sorting machine at speeds of up to 4 m/s and in places even more, and are sorted to their target location by means of appropriately switched diverters and a sophisticated, usually multi-stage delivery route sequence sorting method.
For correct feeding of the postal items it is therefore essential that the address of the postal item can be cleanly read by machine at least at the beginning of the sorting process. Frequently, however, the address cannot be read by the machine but must be added by manually entering the address (or at least the part thereof, which is significant for the current sorting process). This fact makes it necessary that the non-machine-readable postal items have to be channeled out of the sorting process, buffered in a storage module and, after manual assignment of the address, extracted from the store once more and fed into the sorting process.
As well as this, there are naturally a large number of other situations in the sorting process, such as a fault in the sorting path, for example, which make it necessary that postal items have to be temporarily buffered and later fed back into the sorting process.
The storage modules known today, which can contribute to an extensively automated sorting process, usually work on the first-in/first-out principle. The postal items, which are usually transported standing upright and lying on the long edge, are thus accumulated on one side of the stored stack, i.e., on the “top side” of the stack, for example, and extracted from the stack once more on the respective opposite side of the stack (in the terminology chosen in the example, then on the “bottom side”). In doing so, the stacking device acts on the beginning of the stack and the extraction device on the end of the stack, which as a result leads to a kind of tensioned compression spring, which corresponds to the stack of postal items. It is evident that, with this situation, approximately the same average pressure is produced both at the stacking device and also at the extraction device. In order to be able to carry out the task of stacking and extraction reliably, however, different pressures would really be required at the stacking device and at the extraction device. The average pressure that can only be set as a compromise at both ends of the stack therefore leads time and time again to process faults, which manifest themselves, for example, in folding-up or bending or inadequate drawing-in of postal items to the stacking device and faulty extraction or poorly aligned postal items at the extraction device.